2-hydroxy-5-(substituted)phenylalkylaminobenzoic acid derivatives, particularly 2-hydroxy-5-[2-(4-trifluoromethyl phenyl)ethylamino]benzoic acid and its salt, are known to be very useful for treating central nervous system (CNS) diseases such as ischemia, hypoxia, hypoglycemia, traumatic brain injury, traumatic spinal cord injury, epilepsy, Huntington's disease, Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis (U.S. Pat. No. 6,964,982).
As a synthesis method of the 2-hydroxy-5-(substituted)phenylalkylaminobenzoic acid, a preparing method of 2-hydroxy-5-phenylalkylaminobenzoic acid using substitution reaction mechanism performed by reacting aminosalicylic acid and 2-(4-nitrophenyl)ethylbromide or 3-(4-nitrophenyl)propylbromide in a mixture of triethylamine and dimethylformamide (Korean patent laid-open publication No. 2003-0058934).
However, in case of using said method, the intended substitution reaction is unlikely to happen because the amine residue of aminosalicylic acid works as base, and a specific residue of starting material, 2-(4-nitrophenyl)ethylbromide or is likely to be removed as hydrogen bromide, which causes formation of impurities, 4-nitrostyrene or 1-allyl-4-nitrobenzene. In addition, these impurities are difficult to be removed by general recrystallization method.
In addition to the above method, other methods have been disclosed, but all methods disclosed until now have problem that those are not suitable for mass-production.